Printed circuit boards utilize a variety of resists in their manufacture. Typically the resists used are of a temporary or non-permanent type, meaning that the resist is used to create an image and then is later stripped from the surface. Various resists of this type are known and used in the art.
Printed circuit board designs using "permanent resists" are also known. A permanent resist is one which is used to create an image on a surface of the printed circuit board and then remains as an integral part of that surface (ie. is not stripped away). Permanent resists used in the manufacture of printed circuit boards are described in U.S. Pat. No. 3,982,045 issued Sept. 21, 1976 to Kukanskis, the teachings of which are incorporated herein by reference in their entirety. In addition see U.S. Pat. No. 4,882,245 issued to Gelorme et al, the teachings of which are incorporated herein by reference in their entirety. Also see U.S. Pat. Nos. 5,246,817 and 5,322,976, the teachings of which are incorporated herein by reference in their entirety. Shanefield et al., in U.S. Pat. No. 4,444,848, the teachings of which are incorporated herein by reference in their entirety, describes a modified epoxy material which plates with improved adhesion.
Attempts to manufacture useful permanent resists and printed circuit boards and packages using such resists have uncovered a number of difficulties. For a discussion of soldermasks and their compositions please refer to U.S. Pat. No. 5,296,334, the teaching of which are incorporated herein by reference in their entirety. Among the problems experienced are poor adhesion of the resist to the surface, particularly when temperature cycling is taken into consideration, inability to obtain suitable photodefinability of the resist, poor adhesion of subsequent metal platings to the surface of the resist, inability of the resist to withstand processing in the various subsequent processing chemicals, and/or inability of the resist to provide the appropriate dielectric properties necessary.
A permanent resist formulation and process which answered most or all of the above cited drawbacks would prove very beneficial in the fabrication of printed circuit boards, surface laminar circuitry packages and other important devices. Surface Laminar Circuitry ("SLC") is a technique whereby glass/epoxy laminate, or other substrates such as copper laminates, polyimides and polyetherimides, and a permanent resist are used to produce a structure resembling that of a semiconductor integrated circuit. This technology represents a change in the design concept of multilayer boards, and was developed to meet the requirements caused by the increasing rise of surface mounted devices for high resolution boards with high terminal pitch and enhanced wiring capability. It is an object of the current invention to provide such a permanent resist formulation and process.